/Engine/Source/Runtime/CoreUObject/Public/UObject/PackageResourceManager.h
Will return nullptr if the package does not exist or if the PackageResourceManager does not support MappedFilesHandles
IMappedFileHandle* or nullptr
[IMappedFileHandle](API\Runtime\Core\Async\IMappedFileHandle) * OpenMappedHandleToPackage ( const [FPackagePath](API\Runtime\CoreUObject\Misc\FPackagePath) & PackagePath, [FPackagePath](API\Runtime\CoreUObject\Misc\FPackagePath) * OutUpdatedPath )